CGAL users discussion list

[Andreas Fabri <>]

ok, I missed the 'break'.

The code sniplet you show should be ok then, so my guess
is that you there is some bug earlier.

Just the usual question: Do uou use an 
Exact_predicates_inexact_constructions_kernel
or something comparable ?

Add assert(T.is_valid()); right before the for loop.

andreas

Josip Dzolonga wrote:
> I was referring to this
>
> while(!seen.empty()) {
>           for(Finite_vertices_iterator vit = T.finite_vertices_begin();
>                 vit != T.finite_vertices_end(); ++vit) {
>                 if(seen.find(vit->point()) != seen.end()) {
>                     seen.erase(vit->point());
>                     T.remove(vit);
>                     break;
>                 }
>           }
> }
>
> I break the loop after a point is removed. I also tried the code that 
> you provided, but that unfortunately did not solve the problem.
>
> Best,
> Josip
>
>
> On Sun, Nov 15, 2009 at 10:08 PM, Andreas Fabri 
> < 
> <mailto:>> wrote:
>
>     Hi Josip,
>
>     I am not sure you understood my explanantion, but it can also be
>     that I didn't understand yours.
>
>     It is a mistake to do the ++vit, AFTER having called T.remove(vit),
>     and that is what your for loop does.
>
>     My version makes a copy of thr iterator, advances the iterator
>     and only then removes the vertex.
>
>     andreas
>
>
>     Josip Dzolonga wrote:
>
>         Hi Andreas,
>
>         I corrected myself in my latest reply, but that did not solve
>         the problem.
>
>         Josip
>
>         On Sun, Nov 15, 2009 at 9:07 PM, Andreas Fabri
>         
> <
>         
> <mailto:>
>         
> <mailto:
>         
> <mailto:>>>
>  wrote:
>
>            Hi Josip,
>
>            You shouldn't expect that ++vit works correctly after that
>         you called
>            T.remove(vit).
>
>            You better write this
>
>
>            for(Finite_vertices_iterator vit = T.finite_vertices_begin();
>                            vit != T.finite_vertices_end();) {
>
>                            if(seen.find(vit->point()) != seen.end()) {
>                                seen.erase(vit->point());
>                                Vertex_handle vh = vit;
>                                ++vit;
>                                T.remove(vh);
>                                break;
>                            }
>                      }
>
>
>            Note that the same would be true for a std::list.
>
>            andreas
>
>            Josip Dzolonga wrote:
>
>                Hi Nico,
>
>                I thought of that, but at no point I am reusing old cell
>                handles/vertex handles. I thought that while removing them, I
>                might be causing the problem - but even if I change to
>         code to
>                the following, the problems remains
>
>                while(!seen.empty()) {
>                         for(Finite_vertices_iterator vit =
>                T.finite_vertices_begin();
>                               vit != T.finite_vertices_end(); ++vit) {
>                               if(seen.find(vit->point()) != seen.end()) {
>                                   seen.erase(vit->point());
>                                   T.remove(vit);
>                                   break;
>                               }
>                         }
>                }
>
>                That is, I am iterating again over all vertices.
>
>                Thanks,
>                Josip
>
>                On Sun, Nov 15, 2009 at 8:42 PM, Nico Kruithof
>                
> <
>  
> <mailto:>
>         
> <mailto:
>  
> <mailto:>>
>                
> <mailto:
>         
> <mailto:>
>  
> <mailto:
>         
> <mailto:>>>>
>
>                wrote:
>
>                   Hi Josip,
>
>                   The assertion says that the vertex is not contained in
>         the Cell.
>                   When you remove vertices, cells get removed and added when
>                   re-triangulating. Internally, CGAL will reuse the
>         memory of
>                deleted
>                   cells for the new cells. This might be the reason you
>         are getting
>                   the assertion.
>                   -- Nico
>
>
>                   On Sun, Nov 15, 2009 at 6:26 PM, Josip Dzolonga
>                
> <
>  
> <mailto:>
>         
> <mailto:
>  
> <mailto:>>
>                   
> <mailto:
>         
> <mailto:>
>  
> <mailto:
>         
> <mailto:>>>>
>  wrote:
>
>                       Hello everyone,
>
>                       I am trying to remove some certain points from the
>         Delaunay
>                       triangulation. I had some problems even before,
>         and got some
>                       advice from here, but the problem still pertains. The
>                       problematic code follows
>
>                       for(Finite_vertices_iterator vit =
>         T.finite_vertices_begin();
>                                   vit != T.finite_vertices_end(); ++vit) {
>                                   if(seen.find(vit->point()) !=
>         seen.end()) {
>                                       seen.erase(vit->point());
>                                       T.remove(vit);
>                                  }
>                       }
>
>                       Where seen is of type std::set<Point> and has been
>         already
>                       filled. Later on when I try to use the
>         triangulation, I
>                get the
>                       following error
>
>                       CGAL error: assertion violation!
>                       Expr: v == V[3]
>                       File: /usr/include/CGAL/Triangulation_ds_cell_base_3.h
>                       Line: 98
>                       terminate called after throwing an instance of
>                'std::logic_error'
>                         what():  basic_string::_S_construct NULL not valid
>                       Aborted
>
>                       Which comes from the function  int index(const
>         Vertex_handle&
>                       v). I can not remove the same vertex twice, since I am
>                iterating
>                       over the finite vertices and this is the only
>         place where
>                vertex
>                       removal is taking place. Any ideas would be highly
>                appreciated!
>
>                       Best,
>                       Josip
>
>
>
>
>
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